1. Technical Field
The present invention described herein relates to an analysis method for a periodic structure, the method exemplarily performed through non-destructive testing via measurement of reflectance or transmittance.
2. Discussion of Related Art
Generally, to fabricate electronic devices such as semiconductor devices or display devices, processes of cleaning, thin-film growing, photolithography, and thin-film etching are repeated many times to produce consumer products. For example, in the photolithography process, a circuit of a mask where an image to be fabricated is formed and is transferred to a photosensitive material (photoresist) to form a pattern, and the pattern is used as an etch barrier to form a desired circuit on a thin film.
In semiconductor and display devices fabricated by using the photolithography process, desired circuits need to be transferred to the thin film in an accurate shape in each step. This is possible based on the accuracy of the photolithography process. That is, only when the shape of a desired pattern is accurately transferred to a photoresist and the resist layer properly functions as the etch barrier can an accurate circuit be formed on the thin film. That is, the accurate pattern is to be formed by the photoresist before the circuit is formed on the thin film, and this can be confirmed by a testing process.
To test a pattern, a method of optically observing a shape of a semiconductor device using a pattern tester, for example, has been generally used. However, since the resolution of the pattern tester can be insufficient for determining the shapes of “nano-level” patterns that measure only a few nanometers in length, it is difficult to perform an accurate analysis using a pattern tester. To solve such a drawback, in a semiconductor research and production line, a method of analyzing a specific shape using equipment such as an electron microscope has been used.
However, when an electron microscope is used, since a section of a semiconductor device is cut for shape analysis thereof, the fabricated semiconductor device cannot be used again. Moreover, since the measurement is conducted under a vacuum environment, it can take an excessively long time to obtain a result of the measurement. It may also be impossible to select various regions of a sample to be measured. Due to the aforementioned drawbacks, the electron microscope has a limit in its practical use in the production line.
To address the aforementioned drawbacks, technology using an optical measurement method has been developed and includes, for example, an approximation technique called the Effective Medium Approximation (EMA). A calculation method using EMA has a problem in that, since an approximation is obtained by only a volume ratio of constituent substances in a given period, regardless of a detailed shape of a structure, it never distinguishes a detailed shape of the structure. That is, since the shape of each pattern of a circuit with a periodic structure is not specifically distinguished and only the volume ratio of constituent substances in a given period is distinguished, the difference between the real structure and the measured structure is significant. Specifically, in the periodic structure, since the calculation method using the EMA cannot clarify the different periodic structures if their volume ratios are the same, a new optical measurement method is particularly needed.